How to enable Outlook Web Access for a second domain

I have a 2003 SBS server for which the default email domain is example-A.com and I have created a second email domain example-B.com. When loggin on through webmail in example-A with the username and password it is succesfull. When loggin on with the user and password of example-B then I receive this message:

You could not be logged on to Outlook Web Access. Make sure your domain\user name and password are correct, and then try again.

I already reset the password to make sure it's right and also checked that OWA is enabled for that account.

Despite having TWO email domains example-a.com and example-b.com you only have ONE authentication domain, and that is the domain in Active Directory. by putting @example-b.com after the username you will

Can I try and get I slightly better picture.
You are on a single local domain?
And a single exchange server which is accepting mail for domian a & b.?
Users can access emails for both domains when logged on directly to the network?
And you are access OWA for both domains using a single URL?

If all of these are a "yes" then I would say the problem must be user setup.
If you can test with a working user from domain a or create a duplicate test user add a domain-b.com email address to their mail box. You should now be able to access both from a single user logon.
If this is acceptable policy for your company you could give everybody both address and change the default sender adrdress.

If this works then you need to check the AD profile of you domain-b users.
Check on the exchange features tab. The outlook web access is enabled for these users.

Despite having TWO email domains example-a.com and example-b.com you only have ONE authentication domain, and that is the domain in Active Directory. by putting @example-b.com after the username you will be trying to authenticate against a domain that does not exist in AD. Thus it fails.

If you are using Forms Based Authentication on SBS and it is setup correctly then you should only need to put the username (no domain) into the username box OR domain\username where "domain" is the AD domain name.

example:
AD domain name is: DOMAIN

user account 1: user1
email address : user1@domain-a.com

user account 1: user2
email address: user2@domain-b.com

both users should be able to log on with:
username and password
OR
DOMAIN\username and password

Their email address will be whatever is set as the primary address in AD.

you comments make sense, so I just tried to make a new user for both domains. The both worked immediately. So I thought, ok refresh existing accounts (because OWA was setup later). I refreshed it by just changing the default email address in de properties of the user. Changed it from A to B (submit), changed it back to A (submit) and it just worked.

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